Ophthalmology

ABSTRACT

Apparatus for illuminating the retina of an eye. The apparatus includes an illumination device and a lens system. The illumination device and the lens system combine to provide incident illumination from an apparent point source located within the lens system. The apparatus also includes an illumination transfer device. The illumination transfer device has two foci and the apparent point source of the lens system is provided at a first focus point of the illumination transfer device and an eye is accommodated at a second focus point of the illumination transfer device. The illumination transfer device transfers the incident illumination from the apparent point source into the eye to illuminate the retina.

The present invention relates to an apparatus and method forilluminating, imaging and treating the retina of a human eye.

Imaging systems, such as scanning laser ophthalmoscopes (SLOs), maycomprise a large number of optical components, such as laser scanningelements, scan transfer mirrors, laser sources and detectors. The laserscanning arrangement consists of first and second orthogonal scanningelements, which typically include a high speed rotating polygonal mirrorand a motor driven slow speed mirror. These elements are used to createa raster scan pattern of the human retina. The polygon mirror has aplurality of facets and typically provides the vertical scanning of thelaser beam, and the slow speed mirror typically provides the horizontalscanning of the laser beam. The scan transfer mirror transfers the twodimensional laser scan pattern created by the scanning elements to theretina of the eye.

While such imaging systems provide acceptable images of the retina ofthe eye, they are limited in that they are expensive to manufacture (thelaser scanning elements and scan transfer mirror are particularlyexpensive components), large in size and, due to the large number ofoptical components, have low optical efficiency.

According to a first aspect of the present invention there is providedan apparatus for illuminating the retina of an eye comprising:

-   -   an illumination device;    -   a lens system,

wherein the illumination device and the lens system combine to provideincident illumination from an apparent point source located within thelens system; and

-   -   an illumination transfer device, wherein the illumination        transfer device has two foci and the apparent point source of        the lens system is provided at a first focus point of the        illumination transfer device and an eye is accommodated at a        second focus point of the illumination transfer device, and        wherein the illumination transfer device transfers the incident        illumination from the apparent point source into the eye to        illuminate the retina.

The lens system may include an apparent focus point located within thelens system. The lens system may comprise a plurality of lens elements.The apparent focus point may be located within an outermost lens elementof the lens system. The apparent focus point and the apparent pointsource are coincident.

The illumination device and the lens system combine to illuminate anarea of the retina. That is, the illumination device and the lens systemare capable of illuminating a two-dimensional portion of the retina.

The pupillary point of the eye may be accommodated at the second focusof the illumination transfer device.

The front nodal point of the eye may be accommodated at the second focusof the illumination transfer device.

The illumination device and the lens system are arranged such that theapparent point source is stationary. This ensures that the maximumincident illumination is transferred into the eye at the pupillarypoint.

The lens system may include a wide-angle lens. The wide-angle lens mayhave a field of view (FOV) of between 30 degrees and 180 degrees.Preferably the wide-angle lens has a FOV of between 90 degrees and 160degrees. More preferably, the wide-angle lens has a FOV of 120 degrees.The lens system may comprise or consist of a fisheye lens.

The lens system may comprise a plurality of lens elements. The lenssystem may comprise any number and/or type of lenses required to achievethe desired FOV and/or to achieve achromatism across the visiblespectrum.

The apparent point source may be located within any one of the pluralityof lens elements. Preferably, the apparent point source is located inthe outermost lens element facing the illumination transfer device.

The illumination transfer device may comprise a tilted spherical mirror,an aspherical mirror, an elliptical mirror, an ellipsoidal mirror, apair of parabola mirrors, a pair of paraboloidal mirrors or a lenssystem. In the case where the illumination transfer device comprises alens system, the lens system is arranged to provide two foci.

The apparatus may further comprise an illumination relay device. Theillumination relay device may comprise two foci. One foci of theillumination relay device may be coincident with one foci of theillumination transfer device and the other foci of the illuminationrelay device may be coincident with the apparent point source of theillumination device and the lens system. In this arrangement, theillumination relay device is placed between the illumination transferdevice and the lens system. The illumination device and the lens systemagain combine to provide incident illumination from an apparent pointsource located within the lens system, the apparent point source islocated at the first focus point of the illumination relay device andthe second focus of the illumination relay device is coincident with thefirst focus of the illumination transfer device. The retina of the eyeis again illuminated by the illumination transfer device transferringthe illumination from its first focus point to the pupillary point ofthe eye at its second focus.

The illumination relay device may comprise a tilted spherical mirror, anaspherical mirror, an elliptical mirror, an ellipsoidal mirror, a pairof parabola mirrors, a pair of paraboloidal mirrors or a lens system. Inthe case where the illumination transfer device comprises a lens system,the lens system is arranged to provide two foci.

The illumination relay device may have the same geometry as theillumination transfer device.

The illumination relay device has a major axis, which lies on a linejoining the two foci. The illumination transfer device also has a majoraxis, which lies on a line joining the two foci. The illuminationtransfer device and the illumination relay device may be arranged suchthat the major axis of each device are parallel and/or collinear. Thisarrangement corrects for distortions introduced by the illuminationtransfer device. Since the geometry of the illumination relay device isthe same as the geometry of the illumination transfer device, thedistortions can be cancelled out, or at least partially corrected for.

The illumination device may include a light source. The light source mayprovide collimated light.

The light source may include a laser, a light emitting diode (LED), aVertical Cavity Surface Emitting Laser (VCSEL), a super luminescentdiode (SLD), a diode laser, a collimated incandescent lamp, a flash orillumination device or a digital light processing (DLP) projectiondevice.

The light source may provide illumination at one or more differingwavelengths. The light source may provide red light illumination(approximately 650 nm) and/or green light illumination (approximately510 nm).

The light source may be adapted to provide light at a wavelength between450 nm and 1000 nm. Preferably, the light source may be adapted toprovide light at a wavelength between 488 nm and 700 nm. Morepreferably, the light source provides light at a wavelength of between515 nm and 650 nm.

The light source may be adapted to provide light at a power of between500 nWatt and 1 W.

The light source may include one or more light sources of differingwavelengths.

The light source may be configured such that the wavelength of lightprovided is variable.

The light source may be configured such that the power of light providedis variable.

The illumination device may include a two-dimensional scanning devicefor scanning the retina of the eye with collimated light. In thisconfiguration, the illumination device and the lens system combine toprovide a two-dimensional collimated light scan from the apparent pointsource located within the lens system.

The two-dimensional scanning device may comprise a first scanningelement and a second scanning element.

The first and second scanning elements may comprise an oscillatingmechanism. The oscillating mechanism may be a resonant scanner.

The first and second scanning elements may comprise an oscillating planemirror. The oscillating plane mirror may be a galvanometer mirror.

The first and second scanning elements may comprise a rotatingmechanism. The rotating mechanism may be a rotating polygon mirror.

The first and second scanning elements may comprise a line scanningelement. The line scanning element may comprise a laser line scanner.The laser line may be generated by a diffractive optical element,cylindrical lens, or other known means of creating a laser line.

The first and second scanning elements may comprise a combination ofoscillating mechanisms, rotating mechanisms or line scanning elements,as described above.

The two-dimensional scanning device may be a microelectromechanicalsystem (MEMS) scanning element having two axes of rotation. However, itshould be appreciated that the two-dimensional scanning device may beany suitable device which is capable of rotating in at least two axes,which are preferably orthogonal. The scanning device should preferablybe capable of operating at high speed (i.e. above 5 kHz) and provide ahigh amplitude of scan (i.e. up to 180 degrees or more).

The illumination device may further comprise one or more detectors fordetecting the reflected light from the retina. The reflected light fromthe retina may be used to form an image of the retina.

The light detector may include fast photo detectors, such as avalanchephoto diodes (APDs), PIN diodes, photomultiplier tubes (PMT), siliconphoto multipliers (SPM), or similar single point detectors.

The apparatus may further comprise one or more data processing devicesfor displaying, storing and/or combining the obtained images of theretina.

The apparatus may be pivotable between a first position, in which theapparatus may be used to illuminate the first retina of a first eye, anda second position, in which the apparatus may be used to illuminate thesecond retina of a second eye.

According to a second aspect of the invention, there is provided asystem for illuminating the retina of each eye of a patient comprisingtwo apparatuses according to the first aspect of the invention, whereineach apparatus may be capable of illuminating the retina of one eye.

According to a third aspect of the present invention there is provided amethod of illuminating the retina of an eye comprising the steps of:

-   -   providing an illumination device;    -   providing a lens system;    -   using the illumination device and the lens system in combination        to provide incident illumination from an apparent point source        located within the lens system;    -   providing an illumination transfer device having two foci;    -   providing the apparent point source at the first focus point of        the illumination transfer device and an eye at the second focus        point of the illumination transfer device; and    -   using the illumination transfer device to transfer the incident        illumination from the apparent point source into the eye.

The lens system may include an apparent focus point located within thelens system. The lens system may comprise a plurality of lens elements.The apparent focus point may be located within an outermost lens elementof the lens system. The apparent focus point and the apparent pointsource are coincident.

The illumination device and the lens system combine to illuminate anarea of the retina. That is, the illumination device and the lens systemare capable of illuminating a two-dimensional portion of the retina.

The pupillary point of the eye may be accommodated at the second focusof the illumination transfer device.

The front nodal point of the eye may be accommodated at the second focusof the illumination transfer device.

The illumination device and the lens system are arranged such that theapparent point source is stationary. This ensures that the maximumincident illumination is transferred into the eye at the pupillarypoint.

The lens system may include a wide-angle lens. The wide-angle lens mayhave a field of view (FOV) of between 30 degrees and 180 degrees.Preferably the wide-angle lens has a FOV of between 90 degrees and 160degrees. More preferably, the wide-angle lens has a FOV of 120 degrees.The lens system may comprise or consist of a fisheye lens.

The lens system may comprise a plurality of lens elements.

The apparent point source may be located within any one of the pluralityof lens elements. Preferably, the apparent point source is located inthe outermost lens element facing the illumination transfer device.

The illumination transfer device may comprise a tilted spherical mirror,an aspherical mirror, an elliptical mirror, an ellipsoidal mirror, apair of parabola mirrors, a pair of paraboloidal mirrors or a lenssystem. In the case where the illumination transfer device comprises alens system, the lens system is arranged to provide two foci.

The method may comprise the further step of providing an illuminationrelay device comprising two foci. One foci of the illumination relaydevice may be coincident with one foci of the illumination transferdevice and the other foci of the illumination relay device may becoincident with the apparent point source of the illumination device andthe lens system. In this arrangement, the illumination relay device isplaced between the illumination transfer device and the lens system. Theillumination device and the lens system again combine to provideincident illumination from an apparent point source located within thelens system, the apparent point source is located at the first focuspoint of the illumination relay device and the second focus of theillumination relay device is coincident with the first focus of theillumination transfer device. The retina of the eye is again illuminatedby the illumination transfer device transferring the illumination fromits first focus point to the pupillary point of the eye at its secondfocus.

The illumination relay device may comprise a tilted spherical mirror, anaspherical mirror, an elliptical mirror, an ellipsoidal mirror, a pairof parabola mirrors, a pair of paraboloidal mirrors or a lens system. Inthe case where the illumination transfer device comprises a lens system,the lens system is arranged to provide two foci.

The illumination relay device may have the same geometry as theillumination transfer device.

The illumination relay device has a major axis, which lies on a linejoining the two foci. The illumination transfer device also has a majoraxis, which lies on a line joining the two foci. The illuminationtransfer device and the illumination relay device may be arranged suchthat the major axes of each device are parallel and/or collinear. Thisarrangement corrects for distortions introduced by the illuminationtransfer device. Since the geometry of the illumination relay device isthe same as the geometry of the illumination transfer device, thedistortions can be cancelled out, or at least partially corrected for.

The illumination device may include a light source. The light source mayprovide collimated light.

The light source may include a laser, a light emitting diode (LED), aVertical Cavity Surface Emitting Laser (VCSEL), a super luminescentdiode (SLD), a diode laser, a collimated incandescent lamp, a flash orillumination device or a digital light processing (DLP) projectiondevice.

The light source may provide illumination at one or more differingwavelengths. The light source may provide red light illumination(approximately 650 nm) and/or green light illumination (approximately510 nm).

The light source may be adapted to provide light at a wavelength between450 nm and 1000 nm. Preferably, the light source may be adapted toprovide light at a wavelength between 488 nm and 700 nm. Morepreferably, the light source provides light at a wavelength of between515 nm and 650 nm.

The light source may be adapted to provide light at a power of between500 nWatt and 1 W.

The light source may include one or more light sources of differingwavelengths.

The light source may be configured such that the wavelength of lightprovided is variable.

The light source may be configured such that the power of light providedis variable.

The illumination device may include a two-dimensional scanning devicefor scanning the retina of the eye with collimated light. In thisconfiguration, the illumination device and the lens system combine toprovide a two-dimensional collimated light scan from the apparent pointsource located within the lens system.

The two-dimensional scanning device may comprise a first scanningelement and a second scanning element.

The first and second scanning elements may comprise an oscillatingmechanism. The oscillating mechanism may be a resonant scanner.

The first and second scanning elements may comprise an oscillating planemirror. The oscillating plane mirror may be a galvanometer mirror.

The first and second scanning elements may comprise a rotatingmechanism. The rotating mechanism may be a rotating polygon mirror.

The first and second scanning elements may comprise a line scanningelement. The line scanning element may comprise a laser line scanner.The laser line may be generated by a diffractive optical element,cylindrical lens, or other known means of creating a laser line.

The first and second scanning elements may comprise a combination ofoscillating mechanisms, rotating mechanisms or line scanning elements,as described above.

The two-dimensional scanning device may be a microelectromechanicalsystem (MEMS) scanning element having two axes of rotation. However, itshould be appreciated that the two-dimensional scanning device may beany suitable device which is capable of rotating in at least two axes,which are preferably orthogonal. The scanning device should preferablybe capable of operating at high speed (i.e. above 5 kHz) and provide ahigh amplitude of scan (i.e. up to 180 degrees or more).

The method may comprise the further step of providing one or more lightdetectors and using the one or more light detectors to detect reflectedlight from the retina to form an image of the retina. In thisarrangement the method performs the steps of illuminating the retina andobtaining an image of the retina.

The light detector may include fast photo detectors, such as avalanchephoto diodes (APDs), PIN diodes, photomultiplier tubes (PMT), siliconphoto multipliers (SPM), or similar single point detectors.

The method may comprise the further step of pivoting the illuminationdevice, lens system and illumination transfer device between a firstposition, in which illumination of the first retina of a first eye isperformed, and a second position, in which illumination of the secondretina of a second eye is performed.

According to a fourth aspect of the present invention there is providedan apparatus for imaging the retina of an eye comprising:

-   -   an illumination device;    -   a lens system,

wherein the illumination device and the lens system combine to provideincident illumination from an apparent point source located within thelens system;

-   -   a light detector; and    -   an illumination transfer device, wherein the illumination        transfer device has two foci and the apparent point source of        the lens system is provided at a first focus point of the        illumination transfer device and an eye is accommodated at a        second focus point of the illumination transfer device, and        wherein the illumination transfer device transfers the incident        illumination from the apparent point source into the eye to        illuminate the retina and the light detector detects light        reflected from the retina to obtain an image of the retina.

According to a fifth aspect of the present invention there is provided amethod of imaging the retina of an eye comprising the steps of:

-   -   providing an illumination device;    -   providing a lens system;    -   using the illumination device and the lens system in combination        to provide incident illumination from an apparent point source        located within the lens system;    -   providing a light detector;    -   providing an illumination transfer device having two foci;    -   providing the apparent point source at the first focus point of        the illumination transfer device and an eye at the second focus        point of the illumination transfer device;    -   using the illumination transfer device to transfer the incident        illumination from the apparent point source into the eye; and    -   using the light detector to detect light reflected from the        retina to produce an image of the retina.

According to a sixth aspect of the present invention there is providedan apparatus for treating the retina of an eye with collimated lightcomprising:

-   -   a collimated light illumination device;    -   a lens system,    -   wherein the illumination device and the lens system combine to        provide incident collimated light illumination from an apparent        point source located within the lens system; and    -   an illumination transfer device, wherein the illumination        transfer device has two foci and the apparent point source of        the lens system is provided at a first focus point of the        illumination transfer device and an eye is accommodated at a        second focus point of the illumination transfer device, and        wherein the illumination transfer device transfers the incident        collimated light illumination from the apparent point source        into the eye.

Treatment of the retina is interpreted here to include photodynamictherapy, photo-ablation, photoporation, photoactivation or other methodswhere the interaction of the light is used to alter the state orstructure of the retina or to alter the state of chemicals within theretinal structure.

According to a seventh aspect of the present invention there is provideda method of treating the retina of an eye with collimated lightcomprising the steps of:

-   -   providing a collimated light illumination device;    -   providing a lens system;    -   using the illumination device and the lens system in combination        to provide incident collimated light illumination from an        apparent point source located within the lens system;    -   providing an illumination transfer device having two foci;    -   providing the apparent point source at the first focus point of        the illumination transfer device and an eye at the second focus        point of the illumination transfer device; and    -   using the illumination transfer device to transfer the incident        collimated light illumination from the apparent point source        into the eye.

Treatment of the retina is interpreted here to include photodynamictherapy, photo-ablation, photoporation, photoactivation or other methodswhere the interaction of the light is used to alter the state orstructure of the retina or to alter the state of chemicals within theretinal structure.

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings, in which:-

FIG. 1 is a schematic side view of an apparatus for illuminating,imaging and treating the retina of an eye according to the presentinvention;

FIG. 2 is a schematic side view of an alternative apparatus forilluminating, imaging and treating the retina of an eye; and

FIG. 3 is a flowchart diagram detailing a method of illuminating,imaging and treating the retina of an eye according to the presentinvention.

FIG. 1 illustrates an apparatus 10 for illuminating the retina 12 of aneye 14. The apparatus 10 includes an illumination device 16, a lenssystem 18 and an illumination transfer device 20.

The lens system 18 is arranged to include an apparent focus point 23located within the lens system 18. The illumination device 16 and thelens system 18 are arranged such that they combine to provide incidentillumination 22 from an apparent point source 24 located within the lenssystem 18. The apparent focus point 23 of the lens system 18 iscoincident with the apparent point source 24 of the lens system 18. Thefocus point 23 and point source 24 are termed “apparent” because whenthe illumination device 16 illuminates the lens system 18 it appearsthat the incident illumination 22 emanates from an actual, or “real”,point located within the system. That is, if the incident illumination22 were traced back into the lens system 18 without any refraction, itwould appear as if it were emanating from a single point. This is, ofcourse, not true with a wide-angle lens, hence the term “apparent” forboth focus point and point source is used. Importantly, the apparentpoint source 24 is stationary with respect to the lens system 18. Thisensures that the incident illumination 22 emanates from the apparentpoint source 24 without translation.

The incident illumination 22 generated by the illumination device 16 andthe lens system 18 is two-dimensional and therefore illuminates an areaof the retina 12 (see below). The incident illumination 22 in theembodiment illustrated and described here provides a “floodillumination”, i.e. the illumination device 16 simultaneouslyilluminates the area of the retina.

The illumination device 16 includes a light source 26. The light source26 may provide collimated light. The light source 26 may include alaser, a light emitting diode (LED), a Vertical Cavity Surface EmittingLaser (VCSEL), a super luminescent diode (SLD), a diode laser, acollimated incandescent lamp, a flash or illumination device or adigital light processing (DLP) projection device.

The light source 26 is capable of providing illumination at one or morediffering wavelengths. In this arrangement, the light source 26 mayprovide red light illumination (approximately 650 nm) and/or green lightillumination (approximately 510 nm). The light source 26 is capable ofproviding light at a power of between 500 nWatt and 1 W. The wavelengthand power of the light from the light source 26 may both be variable.

As illustrated in FIG. 1, the lens system 18 includes an incidentoptical path 28 and a return optical path 30. The incident optical path28 and a return optical path 30 are split by a beam splitter 32. Thebeam splitter 32 illustrated and described here is 80:20transmission/reflection. However, it should be appreciated that othertypes of beam splitters could be used if required.

The incident optical path 28 includes a first focussing lens 34 and thereturn optical path 30 includes second and third focussing lenses 38, 40and a combined focussing lens and aperture 46. In the embodimentillustrated and described here the return optical path 30 also includesa second (dichroic) beam splitter 48 which splits the returned reflectedlight from the retina 12 to a first detector 50 and a second detector52. As described below, the first detector 50 detects red light and thesecond detector 52 detects green light. It should, however, beappreciated that the apparatus 10 may not necessarily need to includetwo separate colour detectors and that the apparatus 10 may functionequally well with a single detector.

In the embodiment described and illustrated here the lens system 18 is awide-angle lens system which may consist or comprise a fisheye lens. Thelens system 18 is a wide-angle lens comprising a plurality of meniscuslens elements 18 a to 18 e. The wide-angle lens may have a field of view(FOV) of between 30 degrees and 180 degrees. Preferably, the FOV isaround 120 degrees. However, it should be appreciated that thewide-angle lens may have a FOV at any suitable angle between theabove-referenced range depending on the specific requirements of theapparatus 10.

The illumination device 16 and the lens system 18 are arranged such theincident illumination 22 emanates from the apparent point source 24 atan angle α. Angle α is around 120 degrees (see FIG. 1).

The illumination transfer device 20 has two foci 20 a, 20 b. In theembodiment illustrated and described here the illumination transferdevice 20 is an ellipsoidal mirror. However, it should be appreciatedthat the illumination transfer device 20 may alternatively comprise atilted spherical mirror, an aspherical mirror, an elliptical mirror, anellipsoidal mirror, a pair of parabola mirrors, a pair of paraboloidalmirrors or a lens system. In the case where the illumination transferdevice comprises a lens system, the lens system is arranged to providetwo foci.

As illustrated in FIG. 1, the illumination transfer device 20 and thelens system 18 are arranged such that the apparent point source 24 isprovided at the first focus point 20 a of the illumination transferdevice 20 and the eye 14 is accommodated at the second focus point 20 bof the illumination transfer device 20. More specifically, the pupillarypoint 14 a of the eye 14 is positioned at the second focus point 20 b ofthe illumination transfer device 20.

The incident illumination 22 is conveyed to the subject's eye 14 via theillumination transfer device 20. The incident illumination 22 providedat the apparent point source 24 by the illumination device 16 and thelens system 18 is coupled by the illumination transfer device 20 throughthe pupillary point 14 a of the subject's eye 14, and thus onto theretina 12. Thus, the apparatus 10 provides illumination of an area ofthe retina 12.

As stated above, the incident illumination 22 emanates from the apparentpoint source 24 without translation, i.e. the apparent point source 24is stationary during operation. The result of this is that the incidentillumination 22 emerging at the second focus point 20 b of theillumination transfer device 20 is also stationary. The illuminationtransfer device 20 therefore provides “point-to-point” transfer of theincident illumination 22 without translation, or clipping, thereof.Since the illumination transfer device 20 provides point-to-pointtransfer of the incident illumination 22, the incident illumination 22emerging at the second focus point 20 b of the illumination transferdevice 20 emanates therefrom with the same angle α that the incidentillumination 22 emanates from the first focus point 20 a of theillumination transfer device 20, i.e. at an angle of around 120 degrees.

The result of this is that the incident illumination 22 enters the eyewithout being “clipped” by the iris, for example. This maximises thearea of the retina 12 that can be illuminated by the apparatus 10 andallows ultra-wide illumination of the retina 12 to be performed. Asdescribed above, the incident illumination 22 enters the pupillary point14 a of the subject's eye 14 at an angle of around 120 degrees. An angleof around 120 degrees at the pupillary point 14 a of the eye 14 equatesto an angle of around 200 degrees when measured at the centre of the eye14. Therefore, the apparatus 10 can be considered as providing a 120degree “external” angle of illumination and a 200 degree “internal”angle of illumination.

The above-described properties of the illumination device 16, the lenssystem 18 and the illumination transfer device 20 also ensures thatreflected light from the retina is conveyed back through the sameoptical path of the apparatus 10.

The process of illuminating the retina 12 of the eye 14 is illustratedin FIG. 3. With reference to FIG. 3, the retina 12 of the eye 14 may beilluminated by (a) providing the illumination device 16, (b) providingthe lens system 18, (c) using the illumination device 16 and the lenssystem 18 in combination to provide incident illumination from theapparent point source 24 located within the lens system 18, (d)providing the illumination transfer device 20 having two foci 20 a, 20b, (e) providing the apparent point source 24 at the first focus point20 a of the illumination transfer device 20 and an eye 14 at the secondfocus point 20 b of the illumination transfer device 20 and (f) usingthe illumination transfer device 20 to transfer the incidentillumination 22 from the apparent point source 24 into the eye 14.

As described above, the reflected light returned from the retina 12 isdetected at the first and second detectors 50, 52. The reflected lightreturned from the retina 12 is used to produce an image of the subject'sretina 12 in the known manner.

The detectors 50, 52 may include fast photo detectors, such as avalanchephoto diodes (APDs), PIN diodes, photomultiplier tubes (PMTs), siliconphoto multipliers (SPMs), or similar single point detectors.

The apparatus 10 also comprises a data processing device for displaying,processing, storing, and/or combining the obtained images of the retina12. The apparatus 10 may also comprise a distortion correction device,which may be part of the data processing device, for correctingdistortions introduced by the illumination transfer device 20. Theapparatus 10 may also include on or more filed flattener elements whichcorrect for focal aberrations in the system.

FIG. 2 illustrates an alternative embodiment of the apparatus 10. Theonly difference between the apparatus 10 of FIG. 1 and the apparatus 100of FIG. 2 is that an illumination relay device 200 has been placedbetween the lens system 18 and the illumination transfer device 20. Theillumination relay device 200 has the same geometry as the illuminationtransfer device 20.

The illumination relay device 200 has two foci 200 a, 200 b. In theembodiment illustrated and described here the illumination relay device200 is an ellipsoidal mirror. However, it should be appreciated that theillumination relay device 200 may alternatively comprise a tiltedspherical mirror, an aspherical mirror, an elliptical mirror, anellipsoidal mirror, a pair of parabola mirrors, a pair of paraboloidalmirrors or a lens system. In the case where the illumination transferdevice comprises a lens system, the lens system is arranged to providetwo foci.

As illustrated in FIG. 2, the illumination relay device 200, theillumination transfer device 20 and the lens system 18 are arranged suchthat the apparent point source 24 is provided at the first focus point200 a of the illumination relay device 200 and the second focus point200 b of the illumination relay device 200 is coincident with the firstfocus point 20 a of the illumination transfer device 20. The subject'seye 14 is accommodated at the second focus point 20 b of theillumination transfer device 20 as before.

The incident illumination 22 is conveyed to the subject's eye 14 via theillumination relay device 200 and the illumination transfer device 20.The incident illumination 22 provided at the apparent point source 24 bythe illumination device 16 and the lens system 18 is coupled by theillumination relay device 200 to the illumination transfer device 20,which, in turn, couples the incident illumination 22 through thepupillary point 14 a of the subject's eye 14 to the retina 12, asbefore.

Given that the illumination relay device 200 has the same geometry asthe illumination transfer device 20, the illumination relay device 200therefore also provides point-to-point transfer of the incidentillumination 22 without translation, or clipping, thereof. Therefore,the incident illumination 22 emerging at the second focus point 200 b ofthe illumination relay device 200 emanates therefrom with the same angleα that the incident illumination emanates from the first focus point 200a of the illumination relay device 200. It therefore follows that theincident illumination 22 emanating from the fist focus point 20 a of theillumination transfer device 20 (or second focus point 200 b of theillumination relay device 200) emanates with the same angle α as theincident illumination 22 emanating from the second focus point 20 b ofthe illumination transfer device 20 into the eye 14, as before. Theincident illumination 22 therefore again enters the eye 14 without beingclipped, thus maximising the area of the retina 12 that can beilluminated by the apparatus 10. The apparatus 100 again provides a 120degree external angle (200 degree internal angle) of illumination of theretina, as before.

The illumination relay device 200 has a major axis, which lies on a linejoining the two foci (200 a, 200 b). The illumination transfer device 20also has a major axis, which lies on a line joining the two foci (20 a,20 b). The illumination transfer device 20 and the illumination relaydevice 200 may be arranged such that the major axes of each device areparallel and/or collinear.

The purpose of the illumination relay device 200 is to correct fordistortions introduced by the illumination transfer device 20. Since thegeometry of the illumination relay device 200 is the same as thegeometry of the illumination transfer device 20 the distortions can becancelled out, or at least partially corrected for. The arrangement ofthe illumination relay device 200 and the illumination transfer device20 is such that the major axis (i.e. the line joining the two foci ofthe device) of the illumination relay device 200 is parallel andcollinear to the major axis of the illumination transfer device 20. Inthis arrangement the distortions are cancelled by symmetry.

The apparatus 10 may also comprise a distortion correction device, whichmay be part of the data processing device, for correcting distortionsintroduced by the illumination transfer device 20.

The reflected light returned from the retina 12 is detected in the samemanner as described above in relation to the apparatus 10 of FIG. 1. Theapparatus 100 is therefore capable of imaging the retina 12 of the eye14 in the same manner as described above in relation to apparatus 10.

Although the apparatus 10, 100 has been illustrated and described aboveas being used to illuminate and image the retina 12 of a single eye 14of a subject, it should be appreciated that the apparatus 10, 100 may bepivotable between a first position, in which the apparatus 10, 100 maybe used to illuminate and image the first retina of a first eye, and asecond position, in which the apparatus 10, 100 may be used toilluminate and image the second retina of a second eye. In thisarrangement the apparatus 10, 100 may be used to illuminate and imageboth eyes of a subject without the need to move the subject.Alternatively, there may be provided a system for illuminating andimaging the retina of each eye of the patient, whereby the systemcomprises two apparatuses 10, 100, with each apparatus 10, 100 beingused to illuminate and image an eye of the subject.

Although the apparatus 10, 100 has been described above as being used toilluminate and image the retina 12 of the eye 14, it should beappreciated that the apparatus 10, 100 may not necessarily need toproduce an image of the retina 12. That is, the apparatus 10, 100 may beused to simply illuminate the retina 12 without acquiring an image, i.e.not detecting the reflected light from the retina 12. The apparatus 10,100 may therefore be used to treat the retina 12 of the eye 14 byilluminating the retina 12 with light.

The apparatus 10, 100 of the present invention can be manufactured at alower cost than known retinal imaging apparatuses, such as scanninglaser ophthalmoscopes (SLOs), as the apparatus 10, 100 does not requireconventional separated laser scanning elements (i.e. two separateone-dimensional scanning elements separated in space from one another,such as a horizontal scanning polygon mirror and a vertical scanninggalvanometer scanner). Although, as described above, the apparatus 10,100 may use such scanning elements. The apparatus 10, 100 can be mademore compact than known retinal imaging apparatuses, since the apparatus10, 100 uses a smaller number of components. The apparatus 10, 100 ofthe present invention also includes a smaller number of opticalsurfaces, which increases the optical efficiency of the apparatus 10,100. The result of this is that, for the same amount of input power tothe eye, the total power at the imaging detector is higher than knownmethods. Providing a wide-angle lens system 18 in combination with anillumination transfer device 20, as described above, allows the incidentillumination 22 to be provided indirectly to the pupillary point 14 a ofthe eye 14. This allows use of a wide-angle lens system where the“apparent” point source of incident illumination is located within thelens system itself to provide wide-field illumination of the retina. Theapparatus 10, 100 of the present invention thus avoids the need forphysical contact with the eye 14. This is advantageous, as patientsoften find physical contact with retinal illumination apparatusesextremely difficult.

Modifications and improvements may be made to the above withoutdeparting from the scope of the present invention. For example, althoughthe illumination device 16 has been described above as including a lightsource 26 which provides a “flood illumination” to the retina, i.e. theillumination device 16 simultaneously illuminates the area of the retina12, it should be appreciated that alternatively, or additionally, theillumination device 16 may include a two-dimensional scanning device forscanning the retina 12 of the eye 14 with collimated light. In such aconfiguration the illumination device 16 and the lens system 18 combineto provide a two-dimensional collimated light scan from the apparentpoint source 24 located within the lens system 18. The two-dimensionalscanning device may comprise a first scanning element and a secondscanning element. The first and second scanning elements may comprise anoscillating mechanism. The oscillating mechanism may be a resonantscanner. The first and second scanning elements may comprise anoscillating plane mirror. The oscillating plane mirror may be agalvanometer mirror. The first and second scanning elements may comprisea rotating mechanism. The rotating mechanism may be a rotating polygonmirror. The first and second scanning elements may comprise a linescanning element. The line scanning element may comprise a laser linescanner. The laser line may be generated by a diffractive opticalelement, cylindrical lens, or other known means of creating a laserline. The first and second scanning elements may comprise a combinationof oscillating mechanisms, rotating mechanisms or line scanningelements, as described above. Alternatively, the two-dimensionalscanning device may be a microelectromechanical system (MEMS) scanningelement having two axes of rotation. However, it should be appreciatedthat the two-dimensional scanning device may be any suitable devicewhich is capable of rotating in at least two axes, which are preferablyorthogonal. The scanning device should preferably be capable ofoperating at high speed (i.e. above 5 kHz) and provide a high amplitudeof scan (i.e. up to 180 degrees or more). In this arrangement theapparatus 10, 100 would illuminate the retina 12 of the eye 14 byscanning the collimated light across the retina. In this arrangement thewavelength and power levels and variability of the collimated light fromthe scanning device may be the same as described for the floodillumination device. The reflected collimated light may be detected inthe manner described above to produce an image of the retina 12.

Furthermore, although the apparatus 10, 100 has been illustrated anddescribed above as comprising one illumination device 16, it should beappreciated that the apparatus 10, 100 may comprise one or moreillumination devices, which may include one or more light sources and/orone or more two-dimensional scanning devices.

Also, although the apparent focus point 23 and apparent point source 24have been illustrated and described above as being located within theoutermost lens element 18 a of the lens system 18, it should beappreciated that, depending on the arrangement of the lens system 18,the apparent focus point 23 and apparent point source 24 could belocated in one of the other lens elements 18 b to 18 e.

Furthermore, although the FOV of the lens system 18 has been describedabove as being around 120 degrees, it should be appreciated that the FOVof the lens system 18 could be any suitable angle between 30 and 180degrees, for example: 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140,150, 160 or 170, or any value in between these angles.

Also, although the apparatus 100 has been illustrated and describedabove with the illumination relay device 200 being positioned betweenthe lens system 18 and the illumination transfer device 20, it should beappreciated that, since the illumination relay device 200 is essentiallyidentical to the illumination transfer device 20, the apparatus 100 maybe considered has having an illumination relay device 200 beingpositioned between the illumination transfer device 20 and the eye 14.

Furthermore, although the apparatus 10, 100 has been described above asbeing used to illuminate and/or image the retina 12 of the eye 14, itshould be appreciated that the apparatus 10, 100 could be used to treatthe retina of the eye by illuminating the retina with collimated light.In this arrangement, the illumination device 16 would include a sourceof collimated light which may be operated to produce a laser beam ofvariable wavelength and/or power. Furthermore, the source of collimatedlight may be operated to produce a number of differing wavelengths, ifrequired. This allows the apparatus 10, 100 to treat retinal diseases.

Also, although not illustrated or described above, it should beappreciated that, in order to minimise back reflections from the lenssystem 18, the light source 26 would be polarised and the return opticalpath 30 would include a polariser either before or after the aperture46, or alternatively, two separate polarisers before the first andsecond detectors 50, 52. In this arrangement the polarisers would blockthe light directly reflected from the lens system 18 that is notrandomly polarised.

Furthermore, although not illustrated or described above, it should beappreciated that the lens system 18 and/or the illumination transferdevice 20, 200 may be moveable. That is, the lens system 18 and/or theillumination transfer device 20, 200 may be moveable relative to oneanother to compensate for movement in the location of the apparent focuspoint 23 and apparent point source 24 in the lens system 18 whenilluminating and/or imaging the retina 12 at different FOV angles. Whenilluminating and/or imaging the retina 12 at different FOV angles, forexample when illuminating and/or imaging the fundus area of the retina12 and then illuminating and/or imaging the peripheral of the retina 12,the apparent focus point 23 and apparent point source 24 in the lenssystem 18 may move slightly depending on the FOV angle. Arranging thelens system 18 and/or the illumination transfer device 20, 200 such thatthey may be moveable with respect to one another ensures that theapparent focus point 23 and apparent point source 24 of the lens system18 are always accommodated at the first focus point 20 a, 200 a of theillumination transfer device 20, 200. As described above, this preventsthe incident illumination 22 being clipped by the iris when entering theeye.

1. An apparatus for illuminating a retina of an eye, the apparatuscomprising: an illumination device; a lens system; wherein theillumination device and the lens system combine to provide incidentillumination from an apparent point source located within the lenssystem; an illumination transfer device, wherein the illuminationtransfer device has a first focus point and a second focus point and theapparent point source of the lens system is provided at the first focuspoint of the illumination transfer device and the eye is accommodated atthe second focus point of the illumination transfer device; and whereinthe illumination transfer device transfers the incident illuminationfrom the apparent point source into the eye to illuminate the retina. 2.The apparatus according to claim 1, comprising an apparent focus pointlocated within the lens system, wherein the apparent focus point and theapparent point source are coincident.
 3. The apparatus according toclaim 1, wherein the illumination device and the lens system arearranged to illuminate an area of the retina.
 4. The apparatus accordingto claim 1, wherein the lens system includes a wide-angle lens having afield of view (FOV) of between approximately 30 degrees andapproximately 180 degrees.
 5. The apparatus according to claim 1,wherein the illumination transfer device comprises one of the groupconsisting of a tilted spherical mirror, an aspherical mirror, anelliptical mirror, an ellipsoidal mirror, a pair of parabola mirrors, apair of paraboloidal mirrors and a second lens system comprising twofoci.
 6. The apparatus according to claim 1, comprising an illuminationrelay device having a first focus point and a second focus point,wherein the first focus point of the illumination relay device iscoincident with the first focus point of the illumination transferdevice and the second focus point of the illumination relay device iscoincident with the apparent point source of the illumination device andthe lens system; and wherein the illumination relay device transfersincident illumination from the apparent point source to the illuminationtransfer device and the illumination transfer device transfers incidentillumination from the illumination relay device into the eye toilluminate the retina.
 7. The apparatus according to claim 6, whereinthe illumination transfer device and the illumination relay device eachcomprise a major axis which major axis lies on a line joining the focuspoints of the illumination transfer device and the illumination relaydevice, and the illumination transfer device and the illumination relaydevice are arranged such that the major axis of the illuminationtransfer device and the illumination relay device are at least one ofsubstantially parallel and collinear.
 8. The apparatus according toclaim 6, wherein the illumination relay device has substantially thesame geometry as the illumination transfer device.
 9. The apparatusaccording to claim 1, wherein the illumination device comprises a lightsource comprising one of the group consisting of a laser, a lightemitting diode (LED), a Vertical Cavity Surface Emitting Laser (VCSEL),a super luminescent diode (SLD), a diode laser, a collimatedincandescent lamp, a flash or illumination device or a digital lightprocessing (DLP) projection device.
 10. The apparatus according to claim1, wherein the illumination device comprises a two-dimensional scanningdevice for scanning the retina of the eye with collimated light suchthat the illumination device and the lens system are arranged to providea two-dimensional collimated light scan from the apparent point sourcelocated within the lens system.
 11. The apparatus according to claim 10,wherein the two-dimensional scanning device comprises at least one of asingle scanning element capable of rotating in at least two axes and twoseparate scanning elements each having a single axis of rotation. 12.The apparatus according to claim 11, wherein the single scanning elementis a microelectromechanical (MEMS) scanning element.
 13. The apparatusaccording to claim 1, comprising one or more detectors for detecting thereflected light from the retina.
 14. A method of illuminating a retinaof an eye, the method comprising: providing an illumination device;providing a lens system; using the illumination device and the lenssystem in combination to provide incident illumination from an apparentpoint source located within the lens system; providing an illuminationtransfer device having a first focus point and a second focus point;providing the apparent point source at the first focus point of theillumination transfer device and the eye at the second focus point ofthe illumination transfer device; and using the illumination transferdevice to transfer the incident illumination from the apparent pointsource into the eye.
 15. The method according to claim 14, wherein: anapparent focus point is located within the lens system; and the apparentfocus point and the apparent point source are coincident.
 16. The methodaccording to claim 14, wherein the illumination device and the lenssystem are arranged to illuminate an area of the retina.
 17. The methodaccording to claim 14, comprising: providing an illumination relaydevice having a first focus point and a second focus point; and whereinthe first focus point of the illumination relay device is coincidentwith the first focus point of the illumination transfer device and thesecond focus point of the illumination relay device is coincident withthe apparent point source of the illumination device and the lenssystem; and wherein the illumination relay device transfers incidentillumination from the apparent point source to the illumination transferdevice and the illumination transfer device transfers incidentillumination from the illumination relay device into the eye toilluminate the retina.
 18. The method according to claim 17, wherein theillumination transfer device and the illumination relay device eachcomprise a major axis which major axis lies on a line joining the focuspoints of the illumination transfer device and the illumination relaydevice and the illumination transfer device and the illumination relaydevice are arranged such that the major axis of the illuminationtransfer device and the major axis of the illumination relay device areat least one of substantially parallel and collinear.
 19. The methodaccording to claim 17, wherein the illumination relay device hassubstantially the same geometry as the illumination transfer device. 20.The method according to claim 14, comprising providing one or moredetectors to detect reflected light from the retina to form an image ofthe retina.
 21. An apparatus for imaging a retina of an eye, theapparatus comprising: an illumination device; a lens system; wherein theillumination device and the lens system combine to provide incidentillumination from an apparent point source located within the lenssystem; a light detector; and an illumination transfer device, whereinthe illumination transfer device has a first focus point and a secondfocus point and the apparent point source of the lens system is providedat the first focus point of the illumination transfer device and the eyeis accommodated at the second focus point of the illumination transferdevice; and wherein the illumination transfer device transfers incidentillumination from the apparent point source into the eye to illuminatethe retina and the light detector detects light reflected from theretina to obtain an image of the retina.
 22. A method of imaging aretina of an eye, the method comprising: providing an illuminationdevice; providing a lens system; using the illumination device and thelens system in combination to provide incident illumination from anapparent point source located within the lens system; providing a lightdetector; providing an illumination transfer device having a first focuspoint and a second focus point; providing the apparent point source atthe first focus point of the illumination transfer device and the eye atthe second focus point of the illumination transfer device; using theillumination transfer device to transfer incident illumination from theapparent point source into the eye; and using the light detector todetect light reflected from the retina to produce an image of theretina.
 23. An apparatus for treating a retina of an eye with collimatedlight, the apparatus comprising: a collimated light illumination device;a lens system; wherein the illumination device and the lens systemcombine to provide incident collimated light illumination from anapparent point source located within the lens system; and anillumination transfer device, wherein the illumination transfer devicehas a first focus point and a second focus point and the apparent pointsource of the lens system is provided at the first focus point of theillumination transfer device and the eye is accommodated at the secondfocus point of the illumination transfer device; and wherein theillumination transfer device transfers incident collimated lightillumination from the apparent point source into the eye.
 24. A methodof treating a retina of an eye with collimated light, the methodcomprising: providing a collimated light illumination device; providinga lens system; using the illumination device and the lens system incombination to provide incident collimated light illumination from anapparent point source located within the lens system; providing anillumination transfer device having a first focus point and a secondfocus point; providing the apparent point source at the first focuspoint of the illumination transfer device and the eye at the secondfocus point of the illumination transfer device; and using theillumination transfer device to transfer incident collimated lightillumination from the apparent point source into the eye.